RB1 and cancer: Since the Vhl/Trp53/Rb1 mutant autochthonous mouse ccRCC model is characterized by high infiltration of myeloid lineage cells and relatively low numbers of T cells (51) and given recent reports that ATRi and other DNA-damaging therapies can favorably modulate the tumor immune microenvironment toward an antitumor immunological state in other cancer models (52–54), we used flow cytometry to determine the relative fractions of different immune cells in control and M4344 plus cisplatin–treated tumors harvested 2 days after the final M4344 administration.